Narrow-band spectral filter made of W-index and step-index fibers

An all-fiber spectral filter constructed with a W-index fiber, supporting a dominant mode with nonzero cutoff frequency, and a step-index single-clad fiber is proposed and analyzed. The proposed filter offers a spectral width on the order of one nanometer, considerably narrower than that provided by a filter made of two single-clad fibers having the same transmission wavelength. The narrow spectral width is achieved by exploiting a relatively large slope difference between the dispersion characteristics of the W-index and step-index fibers constituting the filter. As an example case, the transmission characteristic of the proposed filter with peak transmission at 1300 nm is calculated and compared with that of a corresponding filter made of two single-clad fibers.<
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